Distribution of brine in grain boundaries during static recrystallization in wet, synthetic halite: insight from broad ion beam sectioning and SEM observation at cryogenic temperature     

Guillaume Desbois  Janos L. Urai  Peter A. Kukla  Uwe Wollenberg  Fabián Pérez-Willard  Zsolt Radí  Sandor Riholm 《Contributions to Mineralogy and Petrology》2012,163(1):19-31

We report observations from room temperature static recrystallization experiments (annealing times from minutes to year) of cold-pressed, synthetic, coarse-grained, wet sodium chloride, prepared by broad ion beam polishing and SEM observations at cryogenic temperature to observe directly the brine in grain boundaries. At all stages of annealing, the majority of the brine in the samples is connected in 2D sections along grain boundaries. Another part of the brine is in isolated brine inclusion arrays along grain boundaries and in brine inclusions left behind by migrating brine-filled grain boundaries. Most of these boundaries are mobile because the aggregate is coarsening. We interpret that the boundaries without observable brine films (<15 nm) and brine inclusion arrays are healed and immobile. Evolution of grain boundary structure involves three major processes. First, dissolution on one side of the grain boundary and precipitation on the other side, resulting in grain boundary migration. Second, the development of facets formed by low-index crystallographic planes of the grains bounding the grain boundary brine. When both sides of a grain boundary are able to develop low-index facets in a thick brine film, the resulting impingement boundary is interpreted to be immobile and may prevent the new grain from migrating into a deformed neighbor. When one side of a faceted boundary consists of low-index crystallographic planes and the other side passively follows this faceted shape along irrational surfaces, the boundary is mobile. Third, the healing of grain boundary brine films, producing solid–solid grain boundaries without resolvable brine films.  相似文献   

Method for Stochastic Inverse Modeling of Fault Geometry and Connectivity Using Flow Data   总被引：1，自引：1，他引：0  

Nicolas Cherpeau  Guillaume Caumon  Jef Caers  Bruno Lévy 《Mathematical Geosciences》2012,44(2):147-168

This paper focuses on fault-related uncertainties in the subsurface, which can significantly affect the numerical simulation of physical processes. Our goal is to use dynamic data and process-based simulation to update structural uncertainty in a Bayesian inverse approach. We propose a stochastic fault model where the number and features of faults are made variable. In particular, this model samples uncertainties about connectivity between the faults. The stochastic three dimensional fault model is integrated within a stochastic inversion scheme in order to reduce uncertainties about fault characteristics and fault zone layout, by minimizing the mismatch between observed and simulated data.  相似文献   

Thermal evolution of Pluto and implications for surface tectonics and a subsurface ocean     

Guillaume Robuchon  Francis Nimmo 《Icarus》2011,216(2):426-439

Determining whether or not Pluto possesses, or once possessed, a subsurface ocean is crucial to understanding its astrobiological potential. In this study we use a 3D convection model to investigate Pluto’s thermal and spin evolution, and the present-day observational consequences of different evolutionary pathways. We test the sensitivity of our model results to different initial temperature profiles, initial spin periods, silicate potassium concentrations and ice reference viscosities. The ice reference viscosity is the primary factor controlling whether or not an ocean develops and whether that ocean survives to the present day. In most of our models present-day Pluto consists of a convective ice shell without an ocean. However if the reference viscosity is higher than 5 × 10¹⁵ Pa s, the shell will be conductive and an ocean should be present. For the nominal potassium concentration the present-day ocean and conductive shell thickness are both about 165 km; in conductive cases an ocean will be present unless the potassium content of the silicate mantle is less than 10% of its nominal value. If Pluto never developed an ocean, predominantly extensional surface tectonics should result, and a fossil rotational bulge will be present. For the cases which possess, or once possessed, an ocean, no fossil bulge should exist. A present-day ocean implies that compressional surface stresses should dominate, perhaps with minor recent extension. An ocean that formed and then re-froze should result in a roughly equal balance between (older) compressional and (younger) extensional features. These predictions may be tested by the New Horizons mission.  相似文献   

An updated insight into the natural attenuation of As concentrations in Reigous Creek (southern France)     

Marion Egal  Corinne Casiot  Guillaume Morin  Franoise Elbaz-Poulichet  Marie-Ange Cordier  Odile Bruneel 《Applied Geochemistry》2010,25(12):1949-1957

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Concurrent tectonic and climatic changes recorded in upper Tortonian sediments from the Eastern Mediterranean     

Cornelia M. Köhler  Wout Krijgsman  Douwe J. J. van Hinsbergen  David Heslop  Guillaume Dupont-Nivet 《地学学报》2010,22(1):52-63

The upper Tortonian Metochia marls on the island of Gavdos provide an ideal geological archive to trace variations in Aegean sediment supply as well as changes in the North African monsoon system. A fuzzy-cluster analysis on the multiproxy geochemical and rock magnetic dataset of the astronomically tuned sedimentary succession shows a dramatic shift in the dominance of 'Aegean tectonic' clusters to 'North African climate' clusters. The tectonic signature, traced by the starvation of the Cretan sediment, now enables to date the late Tortonian basin foundering on Crete, related to the tectonic break-up of the Aegean landmass, at c.  8.2 Ma. The synchronous decrease in the North African climate proxies is interpreted to indicate a change in the depositional conditions of the sink rather than a climatic change in the African source. This illustrates that interpretations of climate proxies require a multiproxy approach which also assesses possible contributions of regional tectonism.  相似文献   

Non-chondritic Sm/Nd ratio in the terrestrial planets: Consequences for the geochemical evolution of the mantle-crust system     

Guillaume Caro  Bernard Bourdon 《Geochimica et cosmochimica acta》2010,74(11):3333-279

Super-chondritic ¹⁴²Nd signatures are ubiquitous in terrestrial, Martian and lunar samples, and indicate that the terrestrial planets may have accreted from material with Sm/Nd ratio higher than chondritic. This contradicts the long-held view that chondrites represent a reference composition for the ¹⁴⁷Sm-¹⁴³Nd system. Using coupled ¹⁴⁶Sm-¹⁴²Nd and ¹⁴⁷Sm-¹⁴³Nd systematics in planetary samples, we have proposed a new set of values for the ¹⁴⁷Sm/¹⁴⁴Nd and ¹⁴³Nd/¹⁴⁴Nd ratios of the bulk silicate Earth (Caro et al., 2008). Here, we revise the Bulk Silicate Earth estimates for the ⁸⁷Rb-⁸⁷Sr and ¹⁷⁶Lu-¹⁷⁶Hf systems using coupled Sr-Nd-Hf systematics in terrestrial rocks. These estimates are consistent with Hf-Nd systematics in lunar samples. The implications of a slightly non-chondritic silicate Earth with respect to the geochemical evolution of the mantle-crust system are then examined. We show that the Archean mantle has evolved with a composition indistinguishable from that of the primitive mantle until about 2 Gyr. Positive ε¹⁴³Nd and ε¹⁷⁶Hf values ubiquitous in the Archean mantle are thus accounted for by the non-chondritic Sm/Nd and Lu/Hf composition of the primitive mantle rather than by massive early crustal formation, which solves the paradox that early Archean domains only have a limited extension in the present-day continents. The Sm-Nd and Lu-Hf evolution of the depleted mantle for the past 3.5 Gyr can be entirely explained by continuous extraction of the continents from a well-mixed mantle. Thus, in contrast to the chondritic Earth model, Sm-Nd mass balance relationships can be satisfied without the need to call upon hidden reservoirs or layered mantle convection. This new Sm-Nd mass balance yields a scenario of mantle evolution consistent with trace element and noble gas systematics. The high ³He/⁴He mantle component is associated with ¹⁴³Nd/¹⁴⁴Nd compositions indistinguishable from the bulk silicate Earth, suggesting that the less degassed mantle sources did not experience significant fractionation for moderately incompatible elements.  相似文献   

Global land water storage change from GRACE over 2002–2009; Inference on sea level     

William Llovel  Mélanie Becker  Anny Cazenave  Jean-François Crétaux  Guillaume Ramillien 《Comptes Rendus Geoscience》2010,342(3):179-188

Global change in land water storage and its effect on sea level is estimated over a 7-year time span (August 2002 to July 2009) using space gravimetry data from GRACE. The 33 World largest river basins are considered. We focus on the year-to-year variability and construct a total land water storage time series that we further express in equivalent sea level time series. The short-term trend in total water storage adjusted over this 7-year time span is positive and amounts to 80.6 ± 15.7 km³/yr (net water storage excess). Most of the positive contribution arises from the Amazon and Siberian basins (Lena and Yenisei), followed by the Zambezi, Orinoco and Ob basins. The largest negative contributions (water deficit) come from the Mississippi, Ganges, Brahmaputra, Aral, Euphrates, Indus and Parana. Expressed in terms of equivalent sea level, total water volume change over 2002–2009 leads to a small negative contribution to sea level of –0.22 ± 0.05 mm/yr. The time series for each basin clearly show that year-to-year variability dominates so that the value estimated in this study cannot be considered as representative of a long-term trend. We also compare the interannual variability of total land water storage (removing the mean trend over the studied time span) with interannual variability in sea level (corrected for thermal expansion). A correlation of ∼0.6 is found. Phasing, in particular, is correct. Thus, at least part of the interannual variability of the global mean sea level can be attributed to land water storage fluctuations.  相似文献   

Observed subsurface signature of Southern Ocean sea level rise   总被引：1，自引：0，他引：1  

Rosemary Morrow  Guillaume Valladeau  Jean-Baptiste Sallee 《Progress in Oceanography》2008,77(4):351-366

Satellite altimetry data show a strong increase in sea level in various parts of the Southern Ocean over the 1990s. In this paper, we examine the causes of the observed sea level rise in the region south of Australia, using 13 years of repeat hydrographic data from the WOCE SR3 sections, and the SURVOSTRAL XBT and surface salinity data. The hydrographic data show a poleward shift in the position of the Subtropical and the Subantarctic Fronts over the period. In the Antarctic Zone, the Antarctic Surface Water has become warmer and fresher, and the Winter Water tongue has become warmer, fresher, thinner and shallower. Increased freshening south of the Polar Front is linked to increased precipitation over the 1990s. Temperature changes over the upper 500 m account for only part of the altimetric sea level rise. The CTD sections show that the deeper layers are also warmer and slightly saltier and the observed sea level can be explained by steric expansion over the upper 2000 m. ENSO variability impacts on the northern part of the section, and a simple Sverdrup transport model shows how large-scale changes in the wind forcing, related to the Southern Annular Mode, may contribute to the deeper warming to the south.  相似文献   

Reactivity at (nano)particle-water interfaces,redox processes,and arsenic transport in the environment     

Laurent Charlet  Guillaume Morin  Jérôme Rose  Yuheng Wang  Mélanie Auffan  André Burnol  Alejandro Fernandez-Martinez 《Comptes Rendus Geoscience》2011,343(2-3):123-139

Massive deleterious impacts to human health are resulting from the use of arsenic-bearing groundwaters in South-East Asia deltas and elsewhere in the world for drinking, cooking and/or irrigation. In Bangladesh alone, a fifth of all deaths are linked to arsenicosis. In the natural and engineered subsurface environment, the fate of arsenic is, to a large extent, controlled by redox potential, pH, as well as total iron, sulfur and carbonate content, via sorption and coprecipitation on a variety of natural and engineered (nano)particles. In the present article, we address: (1) new insights in the sorption mechanisms of As on Fe(II) and Fe(III) nanophases recognized to play an important role in the microbial cycling of As and Fe; (2) artifacts often encountered in field and laboratory studies of As speciation due to the extreme redox sensitivity of the Fe-As-O-H phases; and (3) as a conclusion, the implications for water treatment. Indeed the specific reactivity of nanoparticles accounts not only for the As bioavailability within soils and aquifers, but also opens new avenues in water treatment.  相似文献   

Pollen analyses off Senegal: Evolution of the coastal palaeoenvironment during the last deglaciation     

Anne-Marie Lezine  Jean-Louis Turon  Guillaume Buchet 《第四纪科学杂志》1995,10(2):95-105

Pollen and dinoflagellate cysts from marine sediments in core A180-48 (15°19′N, 18°06′W; 2450 m water depth; 530 cm length) are used to reconstruct palaeoenvironmental conditions of nearshore tropical west Africa during the last deglaciation. High concentrations and influxes of pollen and dinoflagellate cysts between 11 000 and 10 000 yr BP are interpreted as reflecting an increase in continental trade-wind circulation and related coastal upwelling at 15°N latitude. The sea-surface temperature difference between glacial and interglacial times was not as strong as previously suggested. Together with local (fresh) ground-water input, this smaller temperature difference may explain the persistence of the Rhizophora mangrove and Guinean gallery forests near the shore until their massive extension during the early Holocene humid maximum around 9500 yr BP. Pollen data from the core are compared with data from Rosilda N110-Z, from the continental shelf at the same latitude.  相似文献